Lipid and water extracts of many tropical and sub-tropical blue-green algae exhibit good activity against P-388 lymphocytic leukemia and/or Ehrlich ascites tumor in mice. Anticancer compounds will be isolated from those cyanophytes that are easily collected in the field using either P-388 and/or EA bioassays in our laboratory to monitor the fractionations. Molecular structures will be elucidated by a combination of chemical and physical methods. Pure anticancer compounds will be sent to NCI laboratories for chemotherapeutic evaluations. The bis-lactone oscillatoxin A and several related compounds have been isolated from a mixture of cyanophytes identified as Oscillatoria nigroviridis and a Crinalium sp. and the gross structures of these P-388 active toxins have been determined. The absolute stereochemical structures of the oscillatoxins will be elucidated. An indole alkaloid, lyngbyatoxin A, has been found in a variety of Lyngbya majuscula and structure studies will be carried out on this P-388 active compound.